The present invention relates to an X-ray CT apparatus and method, and more particularly to an X-ray CT apparatus and method in which an X-ray tube and an X-ray detector (multi-row detector) are opposed to each other interposing a subject, which detector comprises a multiplicity of X-ray detector elements linearly arranged in the channel arrangement direction to form a plurality of rows in the subject body axis direction, for reconstructing a CT tomographic image of the subject based on detected signals from the X-ray detector.
In the X-ray CT apparatus of this type, since projection data can be simultaneously obtained from the plurality of rows of the multi-row detector in one scan, the speed of X-ray CT imaging can be increased. However, the apparatus cannot be flexibly adapted to imaging for various medical purposes because the scan (projection) data collecting scheme (i.e., a pattern of slices of the subject) is fixed, and improvement is desired.
FIG. 1 is a configuration diagram of the main portion of a conventional X-ray CT apparatus. The apparatus is generally comprised of a scan gantry section 30 for performing an axial/helical scan and reading on the subject by an X-ray fan beam XLFB, an imaging table 20 for supporting the subject 100 and moving the subject 100 in the body axis CLb direction, and an operating console section 10 remotely located for controlling the scan gantry section 30 and imaging table 20, and being operated by, for example, a radiologist.
In the scan gantry section 30, reference numeral 40 designates a rotary anode type X-ray tube, 150 a collimator for limiting the irradiation width of X-rays in the body axis direction, 50A a collimator control section for controlling the slit width xcfx89 of the collimator 150, 70 an X-ray detector (multi-row detector) in which a multiplicity (nxcx9c1,000) of X-ray detector elements are linearly arranged in the channel CH arrangement direction to form four rows L1-L4, for example, in the body axis direction, 80xe2x80x2 a data collecting section (DAS) for generating projection data g(X, xcex8) of the subject based on channel detected signals of the X-ray detector 70 and collecting the data, and 30A a rotation control section for performing rotation control of the X-ray image capturing system (which will be sometimes referred to simply as a gantry hereinbelow). FIG. 1 additionally shows the x-, y- and z-coordinate axes fixed with respect to the scan gantry section 30, where the z-axis coincides with the body axis CLb direction.
In the operating console section 10, reference numeral 11 designates a central processing apparatus for performing main control and processing of the X-ray CT apparatus (such as scan planning, scan control, CT tomographic image reconstruction processing, etc.), 13 a display device (CRT) for displaying the scan plan, the scanned/reconstructed CT tomographic image and the like, 14 a control interface for exchanging several kinds of control signals C1, C2 and monitor signals between the central processing apparatus 11 and the scan gantry section 30 and imaging table 20, and 15 a data collection buffer for accumulating the projection data from the data collecting section 80xe2x80x2.
The operation will be now outlined. The X-ray fan beam XLFB from the X-ray tube 40 passes through the subject 100 and impinges upon all the detector rows L1-L4 of the X-ray detector 70. The data collecting section 80xe2x80x2 generates corresponding projection data g1(X, xcex8)-g4(X, xcex8) by integrating and A/D converting channel detected signal currents of the detector rows L1-L4, and stores the projection data in the data collection buffer 15. Next, similar projection is performed with the gantry slightly rotated to a view angle xcex8, and so forth; thus collecting and accumulating the projection data for one rotation of the gantry.
Moreover, the imaging table 20 is intermittently/continuously moved in the body axis direction of the subject 100 according to an axial/helical scan scheme, and consequently, all the projection data of a required imaged region in the subject are collected and accumulated. The central processing apparatus 11 then reconstructs a CT tomographic image of the subject 100 based on the resulting projection data simultaneously with or after the scan operation, and displays the CT tomographic image on the display device 13.
Inset (a) shows a planar view of the conventional collimator 150. The collimator 150 has a structure such that two parallel slit plates 150a and 150b lying perpendicular to the z-axis are pivotally attached to two links 152a and 152b by pins 154 at the four corners to form a parallelogram, and the links 152a and 152b are pivotally supported by respective pivots 153a and 153b on a centerline CL of the links 152a and 152b. In this configuration, the slit width xcfx89 in the z-axis direction can be changed symmetrically with respect to the centerline CL by swiveling the pivot 153b of the link 152b right and left by a geared motor 155. The centerline CL of the slit width xcfx89 corresponds in position to a centerline CLd of the X-ray detector rows.
The conventional data collecting section 80xe2x80x2 comprises a switch unit (SWU) 81xe2x80x2 that can combine (add) the channel detected signal currents across the detector rows, and a data collecting unit (DAS1-DAS4) 82 that can generate four series of projection data g1(X, xcex8)-g4(X, xcex8) by integrating and A/D converting channel combined currents output from the switch unit 81xe2x80x2. By combining the channel detected signal currents across the detector rows corresponding to a required slice width, the data collecting section 80xe2x80x2 can reconstruct CT tomographic images symmetric with respect to the centerline CLd of the X-ray detector rows and having different slice widths, as will be described below. A conventional scan (projection) data collecting scheme for providing the different slice widths will be particularly described below.
FIG. 2 is a diagram for explaining a conventional data collecting scheme. Specifically, FIG. 2(A) shows a case in which channel detected signal currents i1-i4 of the detector rows L1-L4 are individually converted into projection data S1-S4 having a small slice width by DAS1-DAS4, without combining the channel detected signal currents i1-i4 across the detector rows. Thus, four CT tomographic images having a small slice width can be reconstructed in one scan. This data collecting scheme is suitable for imaging of minute tissues (in the head, lesion site, etc.) of the subject.
FIG. 2(B) shows a case in which channel detected signal currents i1 and i2 of the detector rows L1 and L2, and i3 and i4 of the detector rows L3 and L4 are added (combined) beforehand by the SWU 81xe2x80x2, and then the combined signals are converted into projection data S1 and S2 having a relatively large slice width by, for example, DAS1 and DAS3. Thus, two CT tomographic images having a relatively large slice width can be reconstructed in one scan. This data collecting scheme is suitable for rather minutely checking for the presence of disorder in a relatively large imaged region (thorax, abdomen, etc.) of the subject.
FIG. 2(C) shows a case in which channel detected signal currents i1-i4 of all the detector rows L1-L4 are added (combined) beforehand by the SWU 81xe2x80x2, and then the combined signal is converted into projection data S1 having a large slice width by, for example, DAS1. Thus, one CT tomographic image having a large slice width can be reconstructed in one scan. This data collecting scheme is suitable for broadly checking for the presence of disorder in a large imaging region (thoraxxe2x80x94abdomen, etc.) of the subject. In any case, imaging by the four detector rows can be achieved during one scan, and the speed of the X-ray CT imaging can be increased.
However, since the conventional imaging pattern is symmetric and fixed as described above, it cannot be flexibly adapted to imaging for various medical purposes. Specifically, assume that there are requirements that the presence of disorder should be checked for broadly from the thorax to abdomen of the subject and that the main tissue should be minutely examined. To respond to such requirements in the conventional scheme, imaging with no gap must be performed first from the thorax to abdomen of the subject in the imaging pattern of FIG. 2(C), and then minute imaging of the main site of the subject must be performed in the imaging pattern of FIG. 2(A). Such two-time imaging is time-consuming and, in addition, the subject may be exposed to excessive radiation.
Moreover, since the conventional scheme combines (adds) the channel detected signals (currents) of the X-ray detector elements across the rows as they are, projection data of different slice widths cannot be simultaneously acquired from channel detected signals in a channel. Specifically, when the projection data S1 of FIG. 2(C) is acquired, for example, the projection data S1, S2 or S1-S4 of FIG. 2(B) or (A) cannot be simultaneously acquired. Similarly, when the projection data S1, S2 of FIG. 2(B) is acquired, the projection data S1-S4 of FIG. 2(A) cannot be simultaneously acquired.
The present invention was made considering the aforementioned problems in the prior art, and an object thereof is to provide an X-ray CT apparatus and method that can efficiently acquire projection data having a variety of slice widths (slice patterns) in one scan.
The object can be attained by a configuration shown in FIG. 3, for example. Specifically, in accordance with an aspect (1) of the present invention, there is provided an X-ray CT apparatus in which an X-ray tube 40 and an X-ray detector 70 are opposed to each other interposing a subject 100, in which detector a multiplicity of X-ray detector elements are linearly arranged in the channel arrangement direction to form a plurality of rows in the subject body axis direction, for reconstructing a CT tomographic image of the subject based on detected signals from the X-ray detector, comprising: signal duplicating means 81a for duplicating channel detected signals of the X-ray detector 70 and distributing the duplicated signals to a plurality of groups a, b, etc.; signal combining means 81b that can combine the distributed duplicated signals in each group in an arbitrary pattern across the detector rows for each channel; and data collecting means 82 for converting the channel combined signals for each group into projection data for each channel and collecting the projection data along the channel arrangement direction.
In the aspect (1) of the present invention, the configuration in which the channel detected signals of the X-ray detector 70 are duplicated and distributed to a plurality of groups enables projection data having different slice widths (slice patterns) to be simultaneously acquired for channel detected signals in a channel. Specifically, even when the projection data S1 of FIG. 2(C) is acquired, for example, the projection data S1, S2 or S1-S4 of FIG. 2(B) or (A) can be simultaneously acquired. Moreover, in the aspect (1) of the present invention, the configuration in which the duplicated signals in each of the groups a, b, etc. can be combined in an arbitrary pattern enables projection data having a variety of slice widths (slice patterns) to be simultaneously and efficiently acquired in one scan, and hence, the configuration can be adapted to imaging requirements according to various medical purposes.
The term xe2x80x9cdifferent slice widthsxe2x80x9d refers to a case in which the channel duplicated signals are combined across the detector rows in a continuous manner, and the term xe2x80x9cslice patternxe2x80x9d refers to a case in which the channel duplicated signals are combined across the detector rows in a discontinuous manner (with gaps).
In accordance with another aspect (2) of the present invention, there is provided an X-ray CT apparatus having the same configuration as that set out in the preamble of the foregoing description of the aforementioned X-ray CT apparatus, comprising, as exemplarily shown in FIG. 17, signal duplicating means 81a for duplicating channel detected signals of the X-ray detector 70 and distributing the duplicated signals to a plurality of groups G1-G3, etc; signal combining means 81b that combines the distributed duplicated signals in each group in a predefined pattern across the detector rows for each channel; and data collecting means 82 for converting the channel combined signals for each group into projection data for each channel and collecting the projection data along the channel arrangement direction.
In the aspect (2) of the present invention, although the number of the slice widths (slice patterns) for the channel combined signals is limited, the signal duplicating means 81a and signal combining means 81b having a simple configuration enable projection data having a variety of slice widths (slice patterns) to be simultaneously and efficiently acquired in one scan.
In accordance with another aspect (3) of the present invention, there is provided an X-ray CT apparatus having the same configuration as that set out in the preamble of the foregoing description of the aforementioned X-ray CT apparatus, comprising, as exemplarily shown in FIG. 18, signal duplicating means 81a for duplicating channel detected signals of the X-ray detector 70 and distributing the duplicated signals to a plurality of groups G1-G6, etc; signal combining means 81b that combines the distributed duplicated signals in each group in a predefined pattern across the detector rows for each channel; signal selecting means 81c for further selecting from among the channel combined signals for the groups; and data collecting means 82 for converting the selected channel combined signals for each group into projection data for each channel and collecting the projection data along the channel arrangement direction.
In the aspect (3) of the present invention, the signal duplicating means 81a and signal combining means 81b having a relatively simple configuration enable the channel combined signals having various slice widths (slice patterns) to be generated beforehand, and by the configuration in which the channel combined signals are selected by the signal selecting means 81c, projection data having a variety of slice widths (slice patterns) can be simultaneously and efficiently acquired in one scan.
Preferably, in accordance with another aspect (4) of the present invention, the X-ray CT apparatus as described regarding the aspects (1)-(3) of the present invention further comprises data processing means (CPU) for combining the collected projection data for each group across the detector rows for each channel, as exemplarily shown in FIG. 12(B).
In the aspect (4) of the present invention, projection data having an additional different slice width (slice pattern) can be obtained by having the data processing means combine original projection data having a variety of slice widths (slice patterns) obtained in one scan. Therefore, projection data having a variety of slice widths (slice patterns) can be substantially simultaneously and efficiently acquired in one scan.
Preferably, in accordance with another aspect (5) of the present invention, the X-ray CT apparatus as described regarding the aspects (1)-(3) of the present invention comprises, as exemplarily shown in FIG. 5, image reconstructing means (represented by the CPU 11a) for performing image reconstruction of CT tomographic images based on the data from the data collecting means 82.
In the aspect (5) of the present invention, the data collecting means 82 enables the projection data having a variety of slice widths (slice patterns) to be quickly collected by hardware, and the image reconstructing means (CPU 11a) can exclusively concentrate on its fundamental task of image reconstruction processing. Therefore, the processing load on the CPU can be significantly reduced.
Preferably, in accordance with another aspect (6) of the present invention, in the X-ray CT apparatus as described regarding the aspects (1)-(3) of the present invention, the X-ray detector 70 comprises a multiplicity of X-ray detector elements linearly arranged in the channel arrangement direction to form a plurality of rows of equal detection width in the subject body axis direction, as exemplarily shown in FIG. 14.
Preferably, in accordance with another aspect (7) of the present invention, in the X-ray CT apparatus as described regarding the aspects (1)-(3) of the present invention, the X-ray detector 70 comprises a multiplicity of X-ray detector elements linearly arranged in the channel arrangement direction to form a plurality of rows having different detection widths in the subject body axis direction, as exemplarily shown in FIG. 15.
Preferably, in accordance with another aspect (8) of the present invention, in the X-ray CT apparatus as described regarding the aspects (1)-(3) of the present invention, the signal duplicating means 81a comprises current mirror circuits for duplicating the channel detected signal currents of the X-ray detector elements identically or in a constant ratio, as exemplarily shown in FIG. 6. Thus, one or more duplicated signal currents that are the same as or proportional to a reference current based on a channel detected signal current can be efficiently produced.
Preferably, in accordance with another aspect (9) of the present invention, in the X-ray CT apparatus as described regarding the aspect (1) of the present invention, the signal combining means 81b comprises a plurality of switching means for individually ON/OFF controlling the duplicated signals for each group by an external control signal; and a signal combining circuit for combining output signals from the switching means for each group, as exemplarily shown in FIG. 6. Thus, combined signals can be easily generated in arbitrary combination patterns.
Preferably, in accordance with another aspect (10) of the present invention, in the X-ray CT apparatus as described regarding the aspect (3) of the present invention, the signal selecting means 81c comprises a plurality of switching means for individually ON/OFF controlling the channel combined signals for each group by an external control signal; and a signal combining circuit for combining output signals from the switching means for each group, as exemplarily shown in FIG. 18. Thus, combined signals can be easily selected and further combined in arbitrary combination patterns.
Preferably, in accordance with another aspect (11) of the present invention, the X-ray CT apparatus as described regarding the aspect (1) of the present invention comprises an X-ray detector 70 having k detector rows; and m (xe2x89xa72) signal duplicating/combining units 81a, 81b, etc. including a set of signal duplicating means and signal combining means that can perform signal processing for the k/m detector rows, as exemplarily shown in FIG. 16, so that the signal processing for the k detector rows of the X-ray detector are processed in parallel by the m signal duplicating/combining unit.
In the aspect (11) of the present invention, since a plurality of basic signal duplicating/combining units 81a, 81b, etc. are provided in parallel, the present invention can be easily applied to an X-ray detector 70 having many detector rows.
Preferably, in accordance with another aspect (12) of the present invention, the X-ray CT apparatus as described regarding the aspects (1)-(3) of the present invention comprises collimator means 50 interposed between the X-ray tube 40 and X-ray detector 70 that can change the X-ray beam width in the subject body axis direction asymmetrically on both the sides of a center (CLd) of the X-ray detector in the body axis CLb direction, as exemplarily shown in FIG. 3.
Preferably, in accordance with another aspect (13) of the present invention, in the X-ray CT apparatus as described regarding the aspect (12) of the present invention, the collimator means 50 comprises two parallel slit plates 50a and 50b for limiting the X-ray beam width in the subject body axis direction so that slit widths xcfx89a and xcfx89b formed between respective slit plates and a line assumed to lie on the center CLd of the X-ray detector in the body axis direction can be individually changed, as exemplarily shown in FIG. 4.
Preferably, in accordance with another aspect (14) of the present invention, the X-ray CT apparatus as described regarding the aspects (1)-(3) of the present invention further comprises display means 13A for displaying information about a scan plan, and displays marker information S1, S2, etc. of the subject slice positions and/or slice widths on the display means corresponding to combination patterns across the detector rows specified by previously performed scan planning, as exemplarily shown in FIG. 8. Thus, the radiologist, for example, can easily specify and confirm complex scan plans (parameters) taking different slice widths (slice patterns) into account.
In accordance with another aspect (15) of the present invention, there is provided a projection data collecting method for use with an X-ray CT apparatus having the configuration such as that set out in the preamble of the foregoing description of the aforementioned X-ray CT apparatus, comprising duplicating channel detected signals of the X-ray detector and distributing the duplicated signals to a plurality of groups; combining the duplicated signals in each group in an arbitrary pattern across the detector rows for each channel to generate a series of projection data; and simultaneously collecting the projection data having different slice widths based on the channel detected signals in a channel.
In accordance with another aspect (16) of the present invention, there is provided an X-ray CT imaging method employing the X-ray CT apparatus as described regarding the aspects (1)-(3) of the present invention, comprising the steps of: previously specifying combination patterns of channel detected signals across the detector rows during scan planning; and generating/collecting projection data of corresponding slice patterns by performing combination of the channel detected signals across the detector rows according to the specified combination patterns during a subsequent scan.
As described above, according to the present invention, since projection data having a variety of slice widths (slice patterns) can be efficiently acquired in one scan, the present invention can be flexibly adapted to imaging requirements of various medical purposes, and can greatly contribute to improvement of the speed and convenience in X-ray CT medical services.
Further objects and advantages of the present invention will be apparent from the following description of the preferred embodiments of the invention as illustrated in the accompanying drawings.
FIG. 1 is a configuration diagram of the main portion of a conventional X-ray CT apparatus.
FIG. 2 is a diagram for explaining a conventional data collecting scheme.
FIG. 3 is a diagram for explaining the principle of the present invention.
FIG. 4 is a configuration diagram of the main portion of an X-ray CT apparatus in one embodiment.
FIG. 5 is a diagram showing the configuration of a data collecting/calculating system in one embodiment.
FIG. 6 is a diagram for explaining a data collecting scheme in accordance with a first embodiment.
FIG. 7 is a flow chart of X-ray CT imaging processing in one embodiment.
FIG. 8 is a pictorial diagram of scan parameter specifying processing in one embodiment.
FIG. 9 is a diagram (1) for explaining data collecting patterns in the first embodiment.
FIG. 10 is a diagram (2) for explaining data collecting patterns in the first embodiment.
FIG. 11 is a diagram (3) for explaining data collecting patterns in the first embodiment.
FIG. 12 is a diagram (4) for explaining data collecting patterns in the first embodiment.
FIG. 13 is a diagram (5) for explaining data collecting patterns in the first embodiment.
FIG. 14 is a diagram for explaining data collecting patterns in a second embodiment.
FIG. 15 is a diagram for explaining data collecting patterns in a third embodiment.
FIG. 16 is a diagram for explaining data collecting patterns in a fourth embodiment.
FIG. 17 is a diagram for explaining data collecting patterns in a fifth embodiment.
FIG. 18 is a diagram for explaining data collecting patterns in a sixth embodiment.